1. Field of the Invention
The present invention relates to photographic printers. In particular, the present invention is an improved film cleaning apparatus for removing dust and foreign materials from photographic film prior to and during a print exposure.
2. Description of the Prior Art
In commercial photographic processing operations, exposed, undeveloped photographic film is received from customers for processing. In the past, this exposed photographic film has typically been in the form of strips of photographic film rolled within a container and containing 12, 20, 24 or 36 exposures.
After the photographic film is developed, the photographic images contained in the film (which are generally in the form of negatives) are printed in an edge-to-edge relationship on a continuous web of photosensitive paper by a photographic printer machine. The photographic printer causes high intensity light to be passed through the film and imaged on the photographic print paper to expose the photographic emulsion layers of the paper. The print paper is subsequently processed to produce a print of the image contained in the film.
In many photographic printers, film cleaning apparatus is provided which removes fine dust and other foreign materials from the photographic film prior to printing of that film. Since photographic film is a dielectric material, there is a tendency for static electric charge to be developed on the surface of the film during handling. This static electric charge tends to attract dust to the film surfaces. If the dust is not removed prior to the printing, the dust particles of the negative may appear as imperfections in the resulting print. The smaller the image area of the film and the larger the magnification of the image used to produce the print, the more critical the problem of dust and other foreign material on the film.
One type of film cleaning device which has been used in the past is the 3M film cleaner sold by Minnesota Mining and Manufacturing Company. U.S. Pat. No. 3,644,953 by Christiansen describes a film cleaning apparatus of this type, which has a pair of support members in opposed relationship which define a nip. Two lengths of soft, lint-free wiping cloth extend through the nip and form a part of the path of the film through the film cleaner. In addition, a nuclear ionizing device is typically provided to ionize the air along the path and neutralize static charges on the film.
The film cleaning apparatus of the type described in the Christiansen patent, however, has several shortcomings. First, the apparatus cleans the photographic film at a position upstream from the print gate of the printer. Thu dust and other foreign particles can still reaccumulate on the photographic film between the film cleaning apparatus and the print gate. Second, the film cleaning apparatus in the Christiansen patent is usable only with photographic film which is in the form of a strip or web. It is not suited for cleaning photographic film which is in a disc film format, in which individual image frames located circumferentially about a central hub.
Examples of this disc film format of photographic film are disclosed in the following U.S. patents.
______________________________________ Inventor U.S. Pat. No. ______________________________________ Sethi 4,193,822 Morse 4,208,116 Harvey et al 4,208,117 Sethi et al 4,212,673 Harvey et al 4,255,034 Harvey 4,264,169 Harvey et al 4,268,145 ______________________________________
The need for a highly effective film cleaning apparatus is particularly critical in the case of the disc format photographic film described in the above-mentioned patents. The image area of this type of disc format film is smaller than the image area of 110 format film (which is the smallest of the commonly used strip or web format photographic films). The magnification required to print from disc format film, therefore, is larger than that used with 110 format film, and the undesirable effects of dust on the image area are therefore increased.
In the prior art, there have been manual techniques for removing dust and foreign particles from photographic film prior to printing. One of these techniques has involved the use of a hand-held container from which high velocity air can be emitted. The operator uses the hand-held device to direct a blast of high velocity air onto the surface of the film in order to remove dust. This technique is normally performed when very large image area film formats are being printed. This manual technique is not suited to automatic operation and to the high rates of processing which are typically required in commercial photographic processing operations.
In U.S. Pat. Nos. 4,203,664 by Clifton et al and 4,204,733 by Modney et al, photographic printers are shown in which disc films are handled. Both patents show air nozzles for cleaning the disc film prior to the disc film being moved to another station at which printing occurs.
There is a need for an improved film cleaning apparatus which is applicable both to web and disc format films, which ensures that dust or other foreign material does not reaccumulate on the photographic film between the time that the film is cleaned and the time when a print exposure occurs, and which is consistent with automatic, high speed operation of a photographic printer.